These experiments are part of a thirty-year program of research into brain-behavior relationships. The proposed work inquires into the brain mechanisms by which perceptual processes are modified. In one set of experiments, quantitative spatial and temporal receptive field characteristics of unit electrical responses in the primary visual and auditory systems of the brain are mapped by using gratings of various spatial frequences and white visual and auditory noise as stimuli and correlating stimulus-response relationships by computer. The question is then asked whether electrical stimulation of intrinsic cortex or basal ganglia can alter these spatial or temporal receptive field characteristics. In another series of experiments multiple microelectrodes trodes are chronically implanted into primary visual cortex, prestriate cortex, and inferotemporal cortex. Monkeys are trained in tasks demanding selective attention to one of several dimensions of a multidimensional cue and tasks in which correct responses must be made on the basis of size constancy. Analysis of unit activity is compared with gross electrocortical activity evoked by the stimulus. The results of all of these studies will be applied (but not as part of this proposal) directly to patient populations through established collaborative ventures with UCLA and Pacific Medical Centers. The potential applications deal with: 1) diagnostic techniques using computer analyzed scalp electrical activity obtained in the tasks described for the monkey experiments; and 2) the development of prostheses based on the quantitative characterization of spatial and temporal receptive field characteristics and their modifications obtained in the animal experiments.